The present application is based on Japanese Patent Application No. 2001-135873, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a touch input type reflective liquid-crystal display device thin, lightweight and excellent in display quality.
2. Description of the Related Art
As a related-art reflective liquid-crystal display device having a reflective liquid-crystal display panel, a light source, and an input position detecting touch panel provided on a visual side of the reflective liquid-crystal display panel through the light source, there is know as a reflective liquid-crystal display device in which a side light type light pipe used as a light source is used integrally with a pressure-receiving side base material of a touch panel, the pressure-receiving side base material being formed to have diffusing type light output means by mixing diffusing particles or by printing a diffusing material (unexamined Japanese Patent Publication No. 2000-162594).
Such a reflective liquid-crystal display device using a front light system and having a light source disposed on the visual side is used in a mobile apparatus such as a portable telephone set or a portable personal computer. According to the reflective liquid-crystal display device, emergent light of the light incident on a side surface of the light pipe is reversed by a reflecting layer so that display light obtained thus is viewed through the light pipe and the touch panel. Accordingly, a total reflection type reflecting layer can be used and reflectance can be made high. Hence, the reflective liquid-crystal display device using the front light system has an advantage in that a display image can be made bright compared with a semi-transmissive liquid-crystal display device using a backlight unit and a half mirror.
In the related-art touch input type reflective liquid-crystal display device, there is however a problem that the thickness of the side light type light pipe required for light transmission is so large that the thickness and weight of the liquid-crystal display device become large, and that display through the touch panel may be viewed as if it were present deep in the liquid-crystal display device. Further, there has been another problem that interfacial refection of external light is produced in an air layer interposed between the lower surface of the light pipe and the front surface of the liquid-crystal display panel to thereby lower the contrast of the liquid-crystal display, and that luminance in the viewing direction is low because of shortage of display light made to emerge in a perpendicular direction by the diffusing type light output means.
Further, there have been a problem that failure is easily produced in the touch panel, particularly in a transparent electrode of the touch panel, to thereby result in a short lifetime of the touch panel, and a problem that a display image formed by the reflective liquid-crystal display device is disordered by light-diffusing dots to thereby result in lowering of resolution due to image blurs. The reason why the failure is easily produced in the former problem is conceived as follows. That is, when a pressed position is detected by electrical conduction generated by pressure contact between transparent electrodes disposed so as to face each other through input side and pressure-receiving side base materials, the transparent electrodes are easily damaged and degraded by a concavo-convex structure of the diffusing type light output means given to the pressure-receiving side base material.
As the light output means, there has been known light output means which are formed into a prism structure constituted by prism-like concavo-convex portions disposed in the form of stripes at regular intervals. Even in the light output means having a prism structure, however, stress is concentrated on the apices of prisms in the light output means at the time of inputting because the transparent electrode is also formed to have prism-like concavo-convex portions. In such a manner, the prism structure is easily damaged, so that there arises a problem that the transparent electrode is easily cracked and peeled off to thereby make the life of the touch panel shorter. Further, when the prism structure is broken, the broken structure generates abnormal points of light emission from the light pipe. Accordingly, light leakage toward the visual side is increased so that display quality is considerably lowered. Dust generated and deposited due to the broken structure produces abnormal emission points to thereby cause remarkable lowering of display quality.
An object of the present invention is to develop a touch input type reflective liquid-crystal display device using a front light system in which light incident on a side surface is made to emerge efficiently from the display device with good perpendicular directivity so that the display device is bright in display, free from disorder of a display image, excellent in display quality, long in life, thin in thickness and light in weight.
According to the invention, there is provided a reflective liquid-crystal display device having a reflective liquid-crystal display panel, at least one light source, an optical path control layer, a transparent touch panel, and a transparent adhesive layer in the following configuration. That is, the reflective liquid-crystal display panel includes a liquid-crystal cell, and light-reflecting means. The liquid-crystal cell has a back-side cell substrate made of a support substrate containing at least an electrode, a visual-side cell substrate made of a transparent substrate containing at least a transparent electrode, and a layer of liquid crystal between the two cell substrates disposed so that the electrode sides of the two cell substrates face each other. The light-reflecting means is located on the back side with respect to the liquid-crystal layer of the cell. The reflective liquid-crystal display panel is formed in a manner such that external light incident on an outer surface of the visual-side cell substrate is reflected by the light-reflecting means so that display light transmitted through the liquid-crystal layer is made to emerge from the visual-side cell substrate and viewed. The light source is disposed on at least one of side surfaces of the reflective liquid-crystal display panel. The optical path control layer has a thickness in a range of from 10 to 300 xcexcm and is disposed on an outer surface side of the visual-side cell substrate. The transparent touch panel is provided with a mechanism for detecting an input portion and bonded to an outer side of the optical path control layer through the transparent adhesive layer. The optical path control layer includes light output means formed by arrangement of a plurality of fine grooves each made of a concave portion shaped like an approximate triangle in section. Each of the fine grooves has a length of not larger than 250 xcexcm and a depth of not larger than 50 xcexcm, the depth being not larger than ⅕ as large as the length. Each of the fine grooves has an optical path changing slope, and a steep slope facing the optical path changing slope. The optical path changing slopes is provided so that light incident on the side surface from the light source is reflected toward the back-side cell substrate side. Each of the optical path changing slopes is inclined at an inclination angle in a range of from 35 to 48 degrees to a reference plane of the liquid-crystal display panel. Each of the steep slopes is inclined at an inclination angle of not lower than 60 degrees to the reference plane.
According to the invention, there can be formed a front light mechanism in which the optical path of incident light from the light source disposed on a side surface of the liquid-crystal display panel is changed efficiently in the viewing direction of the liquid-crystal display panel through the light output means of the optical path control layer disposed on the visual side and through the light-reflecting means disposed on the back side, so that the light can be utilized for the liquid-crystal display, and in which incident external light in an external light mode can be used for the liquid-crystal display. There can be also formed a reflective liquid-crystal display device thin in thickness, light in weight and excellent in display quality in an external light-illumination double mode by use of the thin optical path control layer and the light source disposed on the side surface.
Further, on basis of the fact that the light output means are constituted by fine grooves, advantages can be generated as follows. First, moirxc3xa9 due to the interference of the light output means with the arranged pixels hardly occurs, so that the presence of the light output means becomes inconspicuous. Second, the display image is hardly disordered, so that resolution becomes excellent. Third, stress is hardly concentrated on the transparent electrodes in input operation, so that failure is hardly generated in the touch panel and the life of the touch panel becomes long. Fourth, interfacial reflection between the touch panel and the liquid-crystal display panel hardly occurs, so that lowering of the contrast can be prevented.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.